The present invention relates to flat panel display and semiconductor manufacturing equipment. and particularly to a hot plate oven and a method tor baking materials on substrates such as flat panel displays and semiconductor wafers.
Flat panel displays and wafers are baked by placing them in a hot plate oven. Typically, the hot plate oven includes a heated chuck that has a set of three to four proximity pins protruding from the heated chuck to hold the substrate above the heated chuck. Some hot plate ovens have large top doors that expose the substrate to considerable ambient air when the substrate is placed in the oven. In a typical oven used to bake substrates, the thermal environment will be greatly disturbed when the large top door is opened. Thus, after introduction of the substrate in the oven there will be undesirable lag time to achieve thermal equilibrium which slows production. Further, when the large top door opens contamination in the ambient air may be introduced. In addition, when hot plate ovens having large top doors are stacked upon each other they will need large vertical clearance space between each oven to permit placing the wafers through the top of the oven, which in turn leads to a need for large vertical robot travel requirements which raises the total cost of the processing equipment.
Hot plate ovens have used a set of three to four lift pins to lift the substrate off the heater surface to enable robotic handling systems to transfer substrates in and out of the oven. The lift pins do not, however, fully support the substrate in the center which then sags due to substrate's own weight and a high oven temperature. This is a particularly difficult problem for flat panel displays and large size wafers such as 300 mm diameter silicon wafers and for substrates having a high coefficient of thermal expansion. Further, the lift pins become hot in the oven over time and tend to leave an image on the to p of the substrate opposite the contact point of the lift pin on the bottom of the substrate due to the volatility of the solvents used in some of the chemicals (e.g., blue color filter material and polyimides) contained in the coating material. Beyond any appearance related concerns the images indicate the physical characteristic of the substrate have changed in some indeterminate way at and about the image which makes the substrate unacceptable for further processing.